Image registration is a determination of a transformation that aligns locations in one image to locations in another image. In medical imaging, registration is particularly useful to integrate or otherwise correlate information acquired from disparate images. For example, patients images acquired at different times can be compared to understand disease progression, to design therapy strategies, to determine treatment effectiveness, and so on. In another example, patient images can be compared with various reference images (e.g., atlases, normal templates, disease templates, etc.) for diagnostic purposes. While medical imaging technology enables unique views of a patient to be obtained, registration of medical images increases the power of the information.
In a clinical setting, medical image registration can involve intra-subject registration (registration of different images of one patient) and/or inter-subject registration (between different images of different patients or templates). For intra-subject medical imaging, for instance, goals can include tracking disease progression, verifying treatment success, updating contoured or segmented volumes of interest, updating therapy plans, and the like. To achieve these goals, multiple images of a patient can be acquired at different times (e.g., daily, weekly, monthly, etc.). Due to variable patient positioning during imaging, changes due to disease progression or response to therapy, systematic errors in the imaging apparatus, and/or general randomness, the images are not perfectly aligned. Registration corrects the misalignment such that corresponding locations, anatomical structures, etc., between the images are correlated.
According to one example, newly acquired images are registered to a previously acquired image. In this example, each successively obtained image is registered to the same reference image. The reference image can be, for example, a first image acquired of the patient. However, it is to be appreciated that the reverse procedure (i.e., registering previously acquired images or reference images to newly acquired images) can be considered as registering in either direction, i.e. old to new or new to old, provides similar benefits.
Alternatively, each image of the patient can be registered to a reference image not associated with the patient, i.e. an inter-subject registration. For instance, the reference image can be an image selected from a library, such as a representative image or an image generated as a composite or average of multiple images from the library.
However, with any of the techniques described above, a patient image is directly, and individually, registered to the reference image(s) or the reference image(s) are directly and individually registered to the patient image. Errors in identifying corresponding anatomy in two images, i.e. registration errors, can result from differences in how anatomical information is represented in the two images, from imaging system differences, from patient configuration difference, differences in anatomy between different patients, etc. Positional alignment differences can result from registrations of successively obtained images of a patient, even when registered to an identical target.
Accordingly, there is a need for accurate registration mechanisms that reduce variability of alignments from systematic, random, and configuration-based effects.